Thermoplastic polyester resins, such as polyalkylene terephthalate resins, are conventionally used as engineering plastics due to their excellent mechanical, electrical and moldability properties. However, thermoplastic polyester resins are flammable and thus are rendered flame-retardant--usually by means of an organic halogenated flame retardant and a flame-retarding auxiliary component--in situations where the resins are intended to form parts or components to be used in environments where nonflammability is required (e.g., components for electrical or electronic devices).
Reinforcing filler materials, such as glass fibers, are typically incorporated in thermoplastic polyester resin compositions so as to increase their mechanical strength and rigidity where such properties are required in the end use environment. In addition, where certain electrical characteristics are required, for example, arc and tracking resistance properties, polyester resins have been blended with talc or clay in combination with a flame retardant.
However, when a flame retardant or filler is incorporated into thermoplastic polyester resin, its mechanical properties, such as impact resistance and tenacity, are usually deleteriously affected. Thus, when thermoplastic polyester resins are used to form electrical components, such as connectors or timer cases, breakage problems may occur during molding, assembly and/or use. What has been needed therefore is a flame-retardant thermoplastic polyester resin having improved impact resistance and tenacity properties.
In this regard, it has been proposed to blend an impact resistance modifier, such as an elastomer, with thermoplastic polyester resin so as to improve its impact resistance properties. However, the improvements in impact resistance that result from such a proposal are still insufficient in terms of many end-use applications. Moreover, the addition of an elastomer to thermoplastic polyester resin usually is accompanied by diminished rigidity, thermal resistance, and/or electrical properties. Hence, further improvements in this field have been needed.
According to the present invention, a flame-retardant reinforced polyester resin composition containing an organic halogenated flame retardant and a filler is provided which exhibits improved impact resistance and tenacity, without sacrificing the polyester resin's excellent mechanical, electrical and/or thermal resistance properties. More specifically, the present invention is related to a thermoplastic polyester resin composition, which contains an organic halogenated flame retardant, an inorganic filler, and a specific phosphoric ester compound (to be discussed in greater detail below).